According to EU Directive 2007/68/EC the addition of bovine milk has to be labelled. For the detection of bovine milk in foodstuffs, sensitive detection systems are required. Approximately 80% of bovine milk proteins are caseins. β-Lactoglobulin, the major allergen of whey, represents a further 10% of the total protein. Bovine milk is one of the most important allergenic food ingredients, especially for children. Very low amounts of bovine milk can cause allergic reactions, which may lead to anaphylactic shock in severe cases. Because of this, milk allergic persons must strictly avoid the consumption of milk or foods containing milk. In particular, the risk of hidden milk proteins in foods such as sausage, cookies, ready meals or beverages represent a critical problem for milk allergic persons.